PROJECT SUMMARY Asthma results from a complex interplay between genetic background and environmental triggers. The majority of asthma flares are triggered by respiratory viral infections, in particular with human rhinovirus (RV). Asthma is genetically strongly linked to ORMDL3, a protein located in the endoplasmic reticulum with various cellular functions. It is overall incompletely understood how ORMDL3 is functionally related to asthma. One of the functions ORMDL3 has is a key regulatory role in cellular sphingolipid metabolism. ORMDL3 regulates de novo sphingolipid synthesis that is mostly controlled by serine-palmitoyl CoA transferase (SPT). Decreased SPT activity results in airway hyperreactivity, the key feature of asthma, suggesting that this specific metabolic pathway is critically involved in asthma pathogenesis. The genetic ORMDL3 variants that are associated with asthma also increase the association of early respiratory infections with childhood asthma, and have specifically been linked to RV-associated asthma. This proposal will address if responses to RV infections are dependent on cellular sphingolipid composition and if RV infection itself affects cellular sphingolipid homeostasis. Supported by preliminary data that demonstrate enhanced airway reactivity in the context of decreased sphingolipid synthesis following infection with RV and an effect of RV, but not respiratory syncytial virus, on sphingolipid synthesis in airway epithelial cells, two specific aims are proposed to assess the central hypothesis that RV-triggered asthma critically depends on and effects sphingolipid homeostasis: Aim 1 will evaluate the response and interaction of human airway epithelial cells with and without impaired sphingolipid synthesis with RV. Aim 2 will assess the effect of RV in the context of decreased sphingolipid synthesis on airway reactivity and lung immune cells. Overall, these studies will provide the basis for a better understanding of the mechanisms for virally-triggered asthma and may lead to the identification of novel therapeutic targets.